Journal of Materials Processing Technology
ELSEVIER Journal of Materials Processing Technology 52 (1995) 76 82
Real-time data management in a flexible manufacturing system (FMS)
J. Angelva*, P. Piltonen Department of Mechanical Engineering, Production Technology Laborato~,, University of Oulu, P.O. Box 444.
SF-90570, Oulu, Finland
The need for more flexible and efficient data management in manufacturing systems has become obvious. To secure the highest utilization rate and maximum productivity of manufac- turing systems, it is necessary to be able to find the right information at the right time and at the right place: Just In Time. Non production and inefficiency in single operated, stand-along NC-machine tools and other NC-equipment are due largely to humanly caused elapsed times between the receipt of information, the formulation of a decision and the performance of the command.
The advantages of Flexible Manufacturing systems (FMS) are obvious if they are compared to stand-along machines. FMS concepts, hardware and software state of the art, are designed mostly on the idea of centralized control. These types of systems are difficult and expensive to expand and maintain. Centralization makes the FMS dependent on a network and a main computer that might cause troubles with breakdowns.
This paper presents solutions for decentralization and real-time data management of the control system of an FMS. An FMS has to be capable of controlling its resources and its state in real-time and take care of the connections to upper levels of enterprise network (CIM). This leads to the use of real time multi-tasking operating systems and suitable software for system developing. Relational Database Management systems (RDBMS) are very common in adminis- trative use but in process-control information management solutions are still based on tradi- tional ways of programming. Standard RDBMSs offer an easier way to integrate the manufac- turing information system with other computer aided (CA-) subsystems through Local Area Networks (LANs). Dependency on the format in which the data is stored is not so crucial if the strategic decision of the company-wide standard for data management has been approved.
The most useful approach to factory systems integration is the modularity of flexible components that are to be implemented to the system. Only in this way it is possible to design systems that are flexible and expandable also in the future. When the system is implemented the technology is at the certain level and the requirements for the products made in the system are well known. In the future, demands to expand the system with new facilities might become topical. If there is already a modular system it is not a great problem to install new equipment in the system.
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J. Angelva, P. Piltonen / Journal of Materials Processing Technology 52 (1995) 76-82 77
With the introduction of the CIM concept at the workshop level the requirement grows for controlling the information flow with computer assistance, and, as far as possible, automatically. For manufacturers this means that ways must be found to integrate machine-tools, depending upon their use, into the information flow. This applies to stand-alone machines as well as to machines that are linked within a flexible manufacturing system.
Operational control of an FMS is very complicated and involves accessing large static and dynamic data sets; representing machine configuration and characteristics, system status and process plans, and complex control algorithms. The control algo- rithms are structured hierarchically, where an upper level issues commands to a lower level and obtains feedback on the achievement of these commands. Some other manufacturing issues that are dealt with in manufacturing software include cost estimation, employee production efficiency, response to changes and various types of report generation. Other related issues are those that are usually planned beyond the daily operations, such as layout design, capacity and production planning and lot sizing.
2. FMS as a part of CIM-organisation
Flexible manufacturing systems are an important part of production automation and CIM. Benefits of other C-techniques (CAD, CAE, CAPP) would be minimal if the information produced by these systems couldn't be used in the production level. The FM-system has to be able to work as a part of a whole company. To meet these requirements the implementation of the system has to take care of connection to upper-level information networks, data base, production planning and other com- puter-assisted systems.
As a key function to integrate systems at all levels of a company, open-system architecture provides new possibilities for designers. A problem is that a choice has to be made between too many standards that are provided by hardware and software manufacturers.
3. Data management of an FMS
FMS-organisation (Fig. 1) handles a lot of information while running. When an FMS is looked at as a part of CIM it is obvious that all of the data needed in the manufacturing is not necessary in the upper levels of CIM.
Mixture data management together with tool management forms an important unit in flexible manufacturing systems. Both tools and fixtures have a great effect on product quality. This is especially important in FMSs because of the high quality
78 ~L Angelva, P. Piltonen / Journal of Materials Processing Technology 52 (1995) 76 82
I--- Machine tools
I FMS ~--~ -~ MACHINING ~.~ MNConitoring
t . . . . . - Swarf and coolant
r---Presetting -H IMPLEMENTATION I l---'Fixturing
- - - MATERIAL ! i-----Loading/Unloading HANDLING I-----l--Transportation , L..--Storing
" -~ QUALITY ASSUARANCE
- -~ AUXIALIRY FUNCTIONS
- - - - - MAINTENANCE
~_~ Measuring/compensation Thermal displacement elimination High precision facilities Methods
~ Washing Deburring Heat treatment Assembly Swarf and coolant management
~__~ Service Repair Documentation TPM
~_~ Configuration Database Scheduling Tooling management Link to upper level
Fig. 1. FMS organisation.
requirements. Unmanned use of such systems necessitates control based on good data management.
At the control level of an FMS, fixtures are associated with tooling, materials handling and conveying. At the design level the fixtures are handled as pictures that do not always have a true counterpart. Therefore, it is essential to connect the information on designed fixtures with the information on existing fixtures and to deliver the data quickly and explicitly to the operators or the control devices. In an FMS where the pallet routes can be selected and where are many NC machines, etc., this kind of data management constitutes a complicated problem.
J. Angelva, P. Piltonen /Journal of Materials Processing Technology 52 (1995) 76-82 79
Directory ] Usr
[ / P a ~ n s f i g
[/parts/_bed] I/parts/fixtures] I/part.s/fixing elements } ]
. I I I
Fig. 2. Directory hierarchy of Interfix.
Simplifying the FMS control can be done by using code or data carrier identifica- tion systems with different technology to transmit data. The tool data (or part data) is carried to the machining center quickly and reliably with the tool and its data carrier. By code/data carriers it can be ensured also that the right tools are in the right places. By using an identification system the tool setting changes become more effective and the number of breaks of the tools decreases. The utilisation rate and productivity of the manufacturing system increase.
4. Fixture data management
During the conventional CAD/CAM-session for designing fixtures a lot of re- sources are wasted only because of the lack of good connections to the production level. It is possible to solve these problems by developing a system that serves both fixture designers and workshop operators. One way is to use a data management system that runs under FMS-control and is connected to CAD/CAM devices. One example is an interactive menu-based fixture designing system called Interfix (Fig. 2). Advantages achieved by this system are that the necessary data is obtainable directly from the FMS-computer and, therefore, the most recent information of the fixtures and fixture elements in use is available. This information facilities the designer's work by making it possible to re-use old fixture constructions and to evaluate the properties of the various fixture alternatives. Different variations of the fixture can be designed quickly to determine the best design.
5. Tool management using RDBMS
General goals of tool management for an FMS are the same as for the factory at large: to provide the right tools, at the right time, in the right place, to produce the
80 J. Angelva, P. Piltonen /Journal of Materials Processing Technology 52 (1995) 76 82
required volume of parts with the minimum investment in resources. The benefits of tool management in an FMS are generally the following: reduced set-up time, higher spindle utilisation, and increased flexibility for smaller batch sizes, although these depend largely on the automation state of a tool management. To use FMS efficiently, especially in unmanned production, it is essential to have proper tool management. Poor tool management can dramatically reduce the efficiency and flexibility of an FMS.
Requirements of a tool management in an FMS are the following: tool standardisa- tion; a computerised tool-data system; storage, transport, and exchange; tool alloca- tion and scheduling; tool-life monitoring; and purchasing- and accounting-depart- ment interfaces.
As a part of an efficient FMS, the possibilities of using a Relational Database Management System (RDBMS) to manage the tool data have been researched. The main concerns are tool classification, tool database, user interfaces and data transfer through network and DNC.
6. Tool classification
In order to manage different types of tools properly it is essential to identify these tools uniquely. In the classification system every tool has a fixed code based on its function. The same code is used to identify the tool in the database, in NC-programs, in tool magazines, in tool pre-setting, in tool storage, etc. The system can manage up to 10000 different tools.
The coding system is carried out using a four-digits T-code, Fig. 3. The main group describes the geometry of the element to be cut (free hole, tolerance hole, plane, sculptured surface, etc.). The sub-group determines the geometry of the tool. For example a free hole can be made using a twist drill, a solid carbide step drill, etc.
The coding system proves the following advantages: only one tool coding system is needed; tooling data preparation is simplified; tools handling can be carried out more, reliably; the coding of each tool is based on its function; the selection of tools is simplified; it is easier to carry out permanent set-ups; tooling maintenance and purchase becomes clearer; tool shortages and errors in tooling information are reduced.
T X1 X2 X3 X4 I I
I I I F Running number I
Subgroup Main group
Fig. 3. Fixed tool coding using a four-digits T-code.
J. Angelva, P. Piltonen /Journal of Materials Processing Technology 52 (1995) 76 82 81
7. Tool database consideration using RDBMS
When designing a tool database one must take in consideration the structure of a database, what information is needed, who needs the information and where the information is created and stored. The structure of the database has a great effect on the functioning of the database application.
There are many ways of data modelling, that described here being an object- oriented data structure, which is not only suitable for tool management but also for other data management applications in a manufacturing environment. The object- oriented data structure is built according to the objects of the real world. This can be understood as storing real objects by their attributes and relations to other objects in an application-independent database. In this way data modelling is done indepen- dently of application, and leads to a data model that suits all applications needing this data.
8. Tool management system in an FMS
The relational database management system used is called ZIM, made by Zanthe Information Incorporated in Canada, and it runs over the QNX operating system. ZIM is a fully integrated application development environment based on the Entity- Relationship (E-R) data model and it has all of the necessary application development facilities such as a data dictionary, a database, query and update, form's manipulation, report writing, structured programming constructs, import/export and debugging.
The tool database is designed based on the object-oriented data modelling. The object classes used in defining the database tables were the following: the available tools given as an exact description of tools that can be assembled, and are already defined in the database; tools in use given as a description of physically-existing tools that are ready for use or in the magazine of the machine tool; a class and classification system; components of tools, given as a description of components of tools; parts, given as a description of parts to be produced by certain tools; and storage.
By RDBMSs- and graphical windowing-tools it is possible to implement a modular Workshop Cell Controller (WSCC) for an efficient distributed FMS-usage and shop floor data management system. Even real-time, multi-tasking operating utilities can be done by low-cost hardware. Its simplicity makes it suitable for small- and medium- size companies, also. Further, in stand-alone use there is a lack of good data management systems, and the idea is to be able to implement the WSCC to this type of environment also.
The basic benefits of RDBMSs compared to file-structured systems are the follow- ing: the data management functions are more effective; applications can be created and maintained more flexibly; other applications are not depended on the format in
82 J. Angelva, P. Piltonen /Journal of Materials Processing Technology 52 (1995) 76 82
which the data is stored; the cont ro l of d i s t r ibut ion is easier; and connect ions to o ther enterpr i se systems are much easier.
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 P. Piltonen, An FMS control system based on databases, M.S. Thesis, Department of Mechanical Engineering, University of Oulu, Oulu, 1991 (in Finnish).
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